Failures in steel casing, or piping, due to improper heat treatment has long been a problem in well completion. Improperly heat treated casing if placed in service in a borehole will be subject to failure because borehole pressures are too high for the inferior hardness properties of the improperly heat treated casing. Casing may be improperly heat treated in its entirety or in one or more areas along the length of the casing. The minimum length will vary from manufacturer to manufacturer because of the differences in heat treating equipment, but will be about six inches.
Any non-destructive test of such a casing before being set in the well is at best an indirect test. For example, Brinell hardness testers have been used to impart a blow at a certain point on the surface of the casing with a known force and the degree of penetration into the surface is measured. The hardness of the steel at the surface is presumed to be an indication of the hardness of the steel throughout its thickness at that point.